The present invention relates to a layered electrophotographic photoconductor and more particularly to a layered electrophotographic photoconductor comprising an electrically conductive base, a charge transporting selenium-tellurium-halogen alloy layer, and a selenium-tellurium-arsenic-halogen alloy layer.
Conventionally, a variety of selenium photoconductors have been proposed for use in electrophotography. A conventional selenium photoconductor comprises an electrically conductive base and a photoconductive layer consisting of amorphous selenium. This selenium photoconductor exhibits good electric charge reception and charge retention properties in the dark, in comparison with other conventional photoconductors. In particular, since it responds sharply to light waves in a comparatively short wavelength range of shorter than 600 nm, it can be used for various purposes.
However, when the selenium photoconductor is continuously used in a copying process for an extended period of time, with charging and exposure thereof repeated a number of times, light fatigue and charging fatigue are caused. The light fatigue lowers the image density of the image produced by the selenium photoconductor, while the charging fatigue causes toner deposition on the background of the copy image.
As mentioned previously, the selenium photoconductor exhibits its spectral sensitivity in the comparatively short wavelength range of shorter than 600 nm. However, it does not exhibit any substantial spectral sensitivity in the wavelength range of longer than 600 nm. Therefore, it is desired that the spectral sensitivity range of the selenium photoconductor be expanded to a longer wavelength range beyond 600 nm.
Furthermore, in the conventional selenium photoconductor, the amorphous selenium in the photoconductive layer is apt to be crystallized while in use and once such crystallization of selenium takes place, the photoconductor cannot be used any longer for electrophotography. In this sense, concerning the conventional selenium photoconductor, prevention of such crystallization is desired. Moreover, the conventional selenium photoconductor is poor in resistance to physical wear and tear.
In order to improve the spectral sensitivity of the selenium photoconductor, a method of adding tellurium to the selenium photoconductor has been proposed. This method works for sensitizing the selenium photoconductor with the spectral sensitivity thereof expanded to some extent. However, that method has side effects of significantly increasing the light fatigue of the selenium photoconductor while in use, and lowering the charge reception and charge retention capabilities as the content of tellurium in the selenium layer of the photoconductor increases.
Furthermore, the selenium-tellurium photoconductor has a shortcoming in that it tends to be fatigued by repeated charging. In order to improve on the charging fatigue shortcoming of the selenium-tellurium photoconductor, a method of doping the selenium-tellurium alloy with halogen has also been proposed. That method, however, has the additional shortcoming of degrading the charge reception and charge retention capabilities of the selenium-tellurium photoconductor.